Serbian player Janko Tipsarevic is doubtful for the Davis Cup final against defending champion Czech Republic because of injury, adding pressure on Novak Djokovic.

Tipsarevic says he has not recovered from a chronic heel injury in time for the best-of-five series this weekend on an indoor hard court at Belgrade Arena. He says the final decision on whether he will play will be made before Thursday's draw.

Tipsarevic's absence would put pressure on the second-ranked Djokovic, who is on an impressive 22-match winning streak, to win both his singles matches and team up with veteran Nenad Zimonjic in doubles on Saturday.

Djokovic says that despite the exhaustion from the grueling tennis season, he is ready to deliver.